As a scale of semiconductor devices is reduced, a demand on a super thin film is increasingly increased. In addition, as a size of contact holes is reduced, a problem on step coverage is increasingly crucial. To overcome these problems, a method of atomic layer deposition (ALD) has been used as a method for deposition.
In brief, atomic layer deposition is performed as follows: A substrate is exposed to a feed gas supplied inside a chamber, and the feed gas is chemically adsorbed on a surface of the substrate through a reaction of the feed gas and the surface of the substrate to form a mono-atomic layer. However, if the surface of the substrate is saturated with the feed gas, the feed gas excluding the feed gas forming the mono-atomic layer is being physically adsorbed rather than being chemically adsorbed due to non-reactivity between the same ligands. Then, if the substrate is exposed to a purge gas, the feed gas being physically adsorbed on the substrate is removed by the purge gas. Then, if the substrate is exposed to a reaction gas, the reaction gas is reacted with the feed gas being chemically adsorbed on the surface of the substrate through substitution between the feed gas and ligands to form a second layer. The reaction gas that is not reacted with the first layer is being physically adsorbed, and is removed by the purge gas when the substrate is again exposed to the purge gas. At this time, a surface of the second layer is a state capable of reacting with the feed gas. A cycle of the aforementioned processes is repeated until a thin film having a desired thickness is formed.
A substrate processing apparatus for forming such an atomic layer comprises a chamber having a space unit formed therein, and a substrate supporting unit rotatably provided inside the chamber and configured to hold a plurality of substrates. Also, a gas injection device is provided in an upper part of the chamber.
The gas injection device comprises a plurality of gas injection units. More specifically, the gas injection device is configured to have a top lid, a central injection unit having a plurality of gas injection holes coupled to a lower central part of the top lid, and a plurality of processing gas and purge gas injection units having a plurality of gas injection holes coupled to a lower part of the top lid, these injection units are formed as a fan-like shape along a circumference of the central injection unit. The top lid has also a plurality of gas injection holes, and each of gas injection holes is communicated with the gas injection holes formed in each injection unit.
The substrate supporting unit is installed such that it elevates and rotates inside the chamber, so that gases injected from each injection unit may be sequentially supplied to a plurality of substrates during deposition of a thin film. For example, a feed gas is supplied to a substrate at the time when a procedure starts, and subsequently a purge gas, a reaction gas and a purge gas are sequentially supplied to the substrate to achieve deposition of a thin film.
The central injection unit provided in a central part of the gas injection device injects the purge gas to prevent the feed gas and the reaction gas from being mixed at a central part of the substrate supporting unit. However, the purge gas injected from the central injection unit acts to push the feed gas and the reaction gas toward an edge direction of the substrate supporting unit, amounts of the feed gas and the reaction gas are relatively low in the central part of the substrate supporting unit, and residence time is also shortened. Thus, since a thin film is not smoothly deposited on a substrate adjacent the central part among substrates mounted on the substrate supporting unit, it is difficult to deposit a thin film having a desired thickness throughout the substrate. Further, since uniformity of a thin film is decreased, there is a problem that reliability and productivity of devices produced are reduced.